Right click any ribbon or menu or bar, Click "Customize..." (NOT Customize Menu), go to Commands Tab, scroll down to View category, and Rotate View icon is near the top of the Buttons panel. Drag that Button to a ribbon or bar or the heads-up bar.

By Mouse:

Right click in open space (not over a component), select Rotate View in pop-up window.

Note: If you have a 3DConnexion CAD Mouse, it comes with a dedicated middle button for this purpose, so you don't have to use a scroll wheel as a button, which avoids potentially zooming in or out while holding the wheel down.

My install reference is 2018 SP5, but I don't imagine this basic functionality being renamed or moved in 2019. Someone could contradict this assumption with factual observation.